In situ eutrophication stimulates dinitrogen fixation, denitrification, and productivity in Red Sea coral reefs
In situ eutrophication stimulates dinitrogen fixation, denitrification, and productivity in Red Sea coral reefs
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原位富营养化刺激红海珊瑚礁的固氮、反硝化和生产力
DOI：
10.3354/meps13352
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发表时间：
2020-07-09
影响因子：
2.5
通讯作者：
Wild, Christian
中科院分区：
文献类型：
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作者：
El-Khaled, Yusuf C.;Roth, Florian;Wild, Christian
富营养化(即有机营养物质的增加)可能会影响珊瑚礁的功能，但关于其对氮(N)循环的影响及其与海底礁群落生产力的关系的知识很少。因此，我们使用联合乙炔试验，研究了现场操纵的富营养化是如何影响生产力的，以及两种相反的N循环途径(氮[N-2]固定、反硝化)。我们假设富营养化会导致氮固定作用减少，反硝化作用增加。在红海中部进行了8wk的就地营养富集期后，测定了3个主要珊瑚礁功能类群(珊瑚礁沉积物、草坪藻和硬壳珊瑚Pocillo-Pora verrucosa)的N通量和生产力(在培养实验中以暗氧气和光氧气通量衡量)。使用缓释肥料，我们将溶解的无机氮浓度提高到环境浓度的7倍。实验中的营养强化促进了所有功能组的N-2固定和反硝化作用，分别是2-7倍和2-4倍。珊瑚礁沉积物的生产力翻了一番，而草坪藻和疣状藻的生产力保持稳定。因此，我们的数据表明：(1)草坪藻是珊瑚礁中主要的固氮者，而反硝化作用在所有被调查的类群中普遍存在；(2)令人惊讶的是，与我们的假设相反，固氮和反硝化作用都参与了对中度富营养化的响应；(3)刺激的固氮和反硝化作用并不直接受到生产力的影响。我们的发现强调了微生物氮循环在(红海)珊瑚礁中的重要性和无处不在，以及它对富营养化的敏感性。
Eutrophication (i.e. the increase of [in-]organic nutrients) may affect the functioning of coral reefs, but knowledge about the effects on nitrogen (N) cycling and its relationship to productivity within benthic reef communities is scarce. Thus, we investigated how in situ manipulated eutrophication impacted productivity along with 2 counteracting N-cycling pathways (dinitrogen [N-2]fixation, denitrification), using a combined acetylene assay. We hypothesised that N-2-fixation would decrease and denitrification increase in response to eutrophication. N fluxes and productivity (measured as dark and light oxygen fluxes assessed in incubation experiments) were determined for 3 dominant coral reef functional groups (reef sediments, turf algae, and the scleractinian coral Pocillo-pora verrucosa) after 8 wk of in situ nutrient enrichment in the central Red Sea. Using slow-release fertiliser, we increased the dissolved inorganic N concentration by up to 7-fold compared to ambient concentrations. Experimental nutrient enrichment stimulated both N-2-fixation and denitrification across all functional groups 2- to 7-fold and 2- to 4-fold, respectively. Productivity doubled in reef sediments and remained stable for turf algae and P. verrucosa. Our data therefore suggest that (1) turf algae are major N-2-fixers in coral reefs, while denitrification is widespread among all investigated groups; (2) surprisingly, and contrary to our hypothesis, both N-2-fixation and denitrification are involved in the response to moderate N eutrophication, and (3) stimulated N-2-fixation and denitrification are not directly influenced by productivity. Our findings underline the importance and ubiquity of microbial N cycling in (Red Sea) coral reefs along with its sensitivity to eutrophication.